The present invention relates generally to apparatus for controlling shingling of printed products conveyed in sequential order from a rotary printing press and variable rotary cutter to a stacking or handling station, and more particularly to novel mechanism for effecting improved deceleration and shingling as each printed product passes from a first high speed conveyor to a slower speed second conveyor.
The speed and efficiency of a rotary printing press is dependent in part on the delivery system following passage of a printed web from the printing press, through an in-line finishing system, if utilized, and then through a rotary cutter operative to cut or sever the printed web transversely into finished or unfinished printed products which are then conveyed to a stacking or other handling station. A common press repeat length of conventional rotary printers is 223/4 inches which is essentially the circumference of the printing plate cylinder of the press. Other press repeat lengths are also employed. When the press repeat length is a single circumference of the printing plate cylinder, it is a conventional practice to make the knife and anvil cylinders of the rotary cutter twice the diameter of the printing plate cylinder for structural strength purposes. A pair of knife blades carried 180.degree. apart on the periphery of the knife cylinder of the rotary cutter will sever the printed web at the end of each press repeat, assuming there is no blanket or blank gap on the forward end of the press repeat length of web and that the rotational speed of the rotary cutter is in timed relation with the speed of the rotary printing press.
It is a conventional practice to accelerate movement of the severed printed products as they leave the rotary cutter so as to create a space between the trailing edge of each product and the leading edge of the next successive product leaving the rotary cutter. Conventional practice further entails conveying the severed products at the accelerated rate along a first conveyor path, generally defined by juxtaposed parallel runs of conveyor belts moving at the accelerated speed, such as a speed 10% greater than the web speed through the print or blanket cylinders, to a second conveyor path defined by at least one conveyor belt moving at a slower speed. To facilitate shingling of the printed products as they enter and are conveyed by the second conveyor toward a stacking or other handling station, it is desirable that the trailing edge of each successive product be depressed momentarily after the product enters the second conveyor and the trailing edge leaves the first conveyor so that the leading edge of the next succeeding printed product passes over the depressed trailing edge to effect shingling.
One known technique for depressing the trailing edge of each successive printed product leaving the first accelerated-movement conveyor path so as to facilitate shingling is to provide a rotary wheel or arm that is rotated in a generally vertical plane at the same rotational speed as the rotary press and on which is mounted a depressor member operative to engage and depress the trailing edge of each successive printed product as it leaves the first conveyor path and enters the slower speed second conveyor path. This technique assists in effecting shingling as long as the repeat length on the rotary press is a full repeat length or is equal to one-half of a full repeat length. In the latter case, a pair of depressors may be mounted on the carrier spaced 180.degree. apart. Alternatively, the rotational speed of the single depressor carrier may be doubled. This, however, creates a problem in that the depressor member is now moving at a tangential velocity greater than the velocity of the printed product received from the accelerated speed conveyor. This tends to increase the surface speed of the product in conflict with the action of the slower speed second conveyor path which is trying to slow down the speed of the product.
Another problem with prior techniques which utilize a rotary arm carrying one or two diametrically opposed depressor members for depressing the trailing edges of successive products leaving the accelerated-speed conveyor path so as to effect product shingling is that they fail to compensate for situations where the rotary press and rotary cutter are designed to produce trimmed and untrimmed printed products having variable longitudinal lengths measuring a fraction of the press repeat length other than one-half, such as one-third, one-fourth, one-fifth or two-thirds of the printing press repeat length. The latter product lengths are commonly described as resulting from "three-around", "four-around", "five-around", etc., press repeats. Further, the prior techniques for effecting shingling of printed products received from a rotary cutter fail to compensate for any transverse scrap or non-image waste strip generally produced between each press repeat length or of web between individual finished products made from the repeat length of web. As a result, where a plurality of printed products are cut from each press repeat, the point of contact between the prior art depressor member and each successive product takes place progressively closer to the trailing edges of the successive products and may actually engage the leading ends of some of the printed products. This creates cumulative error and significantly inhibits desired shingling between successive printed products as they pass from the accelerated speed conveyor path to the slower conveyor path on the way to a stacker or other handling station.
In addition to depressing the trailing edge of each successive printed product passing from the high speed conveyor to the slower speed conveyor to effect shingling of the products disposed on the slower speed conveyor, it is highly desirable that each product be decelerated as it enters the slower conveyor so as to prevent buckling and wrinkling of the individual products. Known systems for delivering printed products in sequential fashion from a printing press effect deceleration of the products after they have entered a reduced speed belt conveyor from a higher speed belt conveyor by causing the leading edge of each product to enter a nip defined between the reduced speed conveyor belts and at least one idler roller. Simultaneously with the leading edge entering this nip, the trailing edge of the product is pressed against the reduced speed conveyor belts by means of a knock-down arm at the upstream end of the second conveyor. A significant problem with this arrangement is that there is no provision for adjustment of the braking action applied to the products, thus failing to enable adjustment of the braking pressure applied to each printed product. Moreover, this arrangement is limited to use with sheet or printed products having equal gaps between successive products.
Thus, a need exists for an arrangement or mechanism which facilitates shingling of printed products being conveyed from a first relatively high speed conveyor to a reduced speed conveyor disposed downstream from a variable rotary cutter operative to cut variable length printed products from a web received from a rotary printer, each printed product being precisely engaged at its trailing edge in timed relation to entering the reduced speed conveyor so as to depress the trailing edge and effect engagement with a stationary brake pad to both decelerate the product and facilitate shingling of printed products carried by the reduced speed conveyor.